Since being upgraded to the new launcher, I've hard to shut down and restart my computer every time I wanted to launch Minecraft.
When I first try to start the launcher, it works as normal; I can explore it, and start the game.
However, if I exit and then reload the launcher, my game won't start. I can view the launcher, but if I try to play, it just closes and my game doesn't start.
Finally, if I try to load it a 3rd time (or 4th, 5th, etc.) then it doesn't load at all. I know it recognises that I've clicked it, since on my taskbar, it shows it start, and then fade away, without starting anything.
This has been happening to me consistently, since I was upgraded to the new launcher. This effect also seems related to the amount of time my computer has been running for: Occasionally, I can open it twice before it stops working (however I have only seen this after starting Minecraft, and then almost immediately quitting the game, without opening a world). Another time, I waited for 15 minutes after restarting my computer, and it acted as if I had opened it twice - showing the launcher but not starting the game.
It seems to affect all versions of Minecraft.